The formation of scales is a common problem in oil and gas wells. These mineral precipitations are known to form near the wellbore, along the casing and tubing, along pipes and heating coils, and inside pumps and valves. The formation of scales can decrease permeability of the subterranean formation penetrated by the well, reduce well productivity and shorten the lifetime of production equipment. In order to clean scales from wells and equipment it is often necessary to stop the production which is both time-consuming and costly.
Several methods are known in the art for introducing scale inhibitors into production wells. For instance, a liquid scale inhibitor may be included in a fracturing fluid and the fracturing fluid pumped into the formation from the surface. This forces the inhibitor into the targeted zone. Alternatively, liquid or solid scale inhibitors may be included in fracturing fluids as a means to transport the production chemicals into the formation to enhance performance.
Fracturing fluids typically contain a crosslinkable viscosifying polymer and a crosslinking agent. Commonly used viscosifying polymers include underivatized guar, guar derivatives and cellulosic derivatives. Commonly used crosslinking agents are those capable of providing borate ions as well as those agents which contain a metal ion such as aluminum, zirconium, titanium and antimony. Such viscosified fluids form three-dimensional gels.
Conventional scale inhibitors, such as phosphonate or polycarboxylates, are typically only feasible in borate crosslinked fracturing fluids. When used with organometallic crosslinking agents, traditional scale inhibitors cause gel stability problems and render gels with undesirable viscosities. This may be attributable to competition between the scale inhibitors and the water soluble viscosifying polymers for the metal crosslinking agents, producing inefficient complexing and thus poor viscosity enhancement.
Alternative scale inhibitors have been sought which may be used in fracturing fluids containing organometallic crosslinking agents.
It should be understood that the above-described discussion is provided for illustrative purposes only and is not intended to limit the scope or subject matter of the appended claims or those of any related patent application or patent. Thus, none of the appended claims or claims of any related application or patent should be limited by the above discussion or construed to address, include or exclude each or any of the above-cited features or disadvantages merely because of the mention thereof herein.
Accordingly, there exists a need for improved scale inhibitors useful in well treatment fluids containing a viscosifying polymer and an organometallic crosslinking agent having one or more of the attributes or capabilities described or shown in, or as may be apparent from, the other portions of this patent.